1. Field of the Invention
The present invention relates to an uninterruptible power supply (UPS), and more particularly to a UPS having an integrated transformer with a commonly shared winding, and reducing turns of the winding and the size and cost of the transformer.
2. Description of the Related Art
Uninterruptible power supplies (UPS) are the power backup equipment serving to supply backup power to power-consuming equipment when the AC mains is abnormal, such as power outage, overvoltage/undervoltage, occurrence of surge current and the like, so as to continuously supply an operating power to the power-consuming equipment and prevent some mission-critical equipment, such as computers, telecommunication networks, private branch exchanges (PBX) and the like, from losing data or getting out of control.
With reference to FIG. 6, a conventional UPS has a surge cancellation and electromagnetic interference (EMI) prevention device 81, a charger 82, a battery set 83, a full-bridge converter 84 and an automatic voltage regulator (AVR) 85.
The surge cancellation and EMI prevention device 81 has an input terminal and an output terminal. The input terminal of the surge cancellation and EMI prevention device 81 is connected with the AC mains.
The charger 82 has an input terminal and an output terminal. The input terminal of the charger 82 is connected with the output terminal of the surge cancellation and EMI prevention device 81.
The battery set is connected with the output terminal of the charger 82.
The full-bridge converter 84 has four power switches G1, G2, G3 and G4, a transformer T and a controller (not shown). Each of the two power switches G1 and G3 and the other two power switches G2 and G4 are connected in pairs. The transformer T has a primary winding and a secondary winding. Two ends of the primary winding are respectively connected to the two pairs of the power switches. The secondary winding has two sub-windings separated from each other.
The automatic voltage regulator 85 has two switches 851, 852. Each switch 851, 852 has two contact points and one common point. The common point is selectively connected with one of the contact points of a corresponding switch 851, 852. The connected contact points of the switches 851, 852 are further connected to the secondary winding of the transformer T. The common point of the switch 851 is serially connected with an input switch and is further connected to the output terminal of the surge cancellation and EMI prevention device 81. The common point of the other switch 852 is connected to a power output terminal.
The power output terminal is connected to a power-consuming equipment. When the AC mains is normal, the mains power not only charges the battery set 83 through the surge cancellation and EMI prevention device 81 and the charger 82 but also directly supplies power to the power-consuming equipment through the automatic voltage regulator 85. When the AC mains fails or is abnormal, the power switches G1, G2, G3 and G4 of the full-bridge converter 84 are driven by the controller to convert the DC power from the battery set 83 into AC power in collaboration with the transformer T and supplies the AC power to the power-consuming equipment. The automatic voltage regulator 85 is also under the control of the controller to boost or buck voltage under a battery mode.
Currently the full-bridge converter 84 usually adopts an isolation transformer. The isolation transformer has a primary winding and a secondary winding. The so-called isolation transformer means that the primary winding and the secondary winding are fully insulated and isolated. To ensure that the primary winding and the secondary winding are fully isolatedly insulated, besides being insulated, the primary winding and the secondary winding should be spaced with a safe distance from each other. Meanwhile, the turns of windings cannot be further reduced. Accordingly, the size and cost of the transformer cannot be effectively reduced.
With reference to FIG. 7, another conventional UPS is shown. The UPS differs from the foregoing conventional UPS in that it adopts a push pull converter 86. The push pull converter 86 has two power switches G1, G2, a transformer and a controller (not shown). The two power switches G1, G2 are controlled by the controller and are connected with the primary winding of the transformer T. The other difference lies in that an input terminal of the charger 82 is connected with a primary auxiliary winding of the transformer T to acquire an operating power for the purpose of charging.
The UPS having the push pull converter 86 still adopts an isolation transformer, and the same bulky problem of the UPS adopting the full-bridge converter is still present. Furthermore, besides having two sub-windings, the primary winding of the transformer further has an auxiliary winding. As all the sub-windings and the auxiliary winding on the primary side are required to be independent and completely insulated and isolated, the size and cost of the UPS cannot be effectively reduced.